Cell Phone Lockers at Work

So I work in a day care in New Jersey, US and we have lockers to put our cellphones. In our first work meeting they said that we can keep our phones in our cars but then after an employee put pictures on Snapchat of two kids they said because of liability issues, our phones HAVE to be in the lockers. They sent out a policy form for us to sign which I never did.

Now anytime my phone is in my car they tell me to go get it and put it in my locker. I wanna know if that's allowed or legal as it is my personal property. It's not on me nor am I using it.

Edit: I just checked my new policy form (the one I haven't signed yet) and it doesn't say anything about cell phones. In the previous one it just says that if we are caught with our cell phones on us while on the clock we will be terminated immediately. So I never signed anything that said it has to be in the lockers and not in the cars. Also I am trying to leave but I wanna know what I can say to my boss if she tried to make me get my phone again so they can't fire me.